Digital Selective Reversible Phase Control of Monolithically Integrated Heterogeneous Piezoelectric Polymer for Frequency Dependent Unimorph

Abstract

Thanks to spontaneous polarization in molecular structure, piezoelectric polymer, poly(vinylidene fluoride) (PVDF) holds great potential for diverse applications such as organic memory and electromechanical devices. However, the transformation of PVDF into a highly polarized beta-phase has still relied on conventional processes such as repeated mechanical strain, high-temperature heat treatment, and high-voltage electric poling, which are time-consuming and can potentially cause undesired damages. Here, an ultrafast and reversible digital patterning process to transform the polymorphic phase of the PVDF has been developed using the interaction of laser with molecular structure. Plasmonic gold nanoparticles realize the interaction between PVDF and laser by increasing the absorption of the laser and amplifying its characteristics. The parameters of the laser process for phase conversion are designed under the theoretical background based on molecular dynamics (MD) simulation, and through this, the process is able to freely convert phases by simple parameter modifications. The selective laser process enables a monolithically integrated heterogeneous phase of PVDF which is not allowed in conventional single-phase producing processes. Moreover, a practical soft robot that can control its direction has been developed by utilizing the difference in mechanical responses of each phase to the electric field in a monolithically integrated single functional layer.